Effluent energy recovery system

ABSTRACT

A septic system thermal recovery mechanism includes a septic tank. The tank has a top, a bottom, and at least one upstanding side wall joining the top to the bottom. The top, bottom, and at least one sidewall define an interior of the tank, and the at least one sidewall is devoid of angular corners. A septic inlet is adapted and constructed to conduct septic waste material into the interior of the tank, and a septic outlet is adapted and constructed to conduct septic waste material out of the interior of the tank. A thermal exchange fluid conduit is embedded in the at least one wall of the tank The thermal exchange fluid conduit is connected to a source of thermal exchange fluid. The mechanism is configured such that thermal exchange fluid can be circulated through the thermal exchange fluid conduit without traversing an angular corner and without contacting the interior of the tank The sidewall can be provided as a cast concrete wall, with the thermal exchange fluid conduit being PVC tubing embedded in sidewall in a spiral configuration at the time the sidewall is cast. The sidewall itself can be configured in any suitable form, such as a substantially contiguous cylindrical wall, or four walls in two substantially parallel pairs of sidewalls, the contiguous sidewalls being connected together with rounded connecting portions. The thermal recovery mechanism can also include a second thermal exchange fluid conduit embedded in the top of the tank. In an embodiment, the mechanism can include first and second tanks constructed as described, with septic waste flowing from the first tank to the second tank. A thermal exchange fluid pump can be connected to circulate thermal exchange fluid sequentially through a return conduit, into a thermal exchange fluid conduit in the second tank, then through a first thermal exchange fluid conduit in the first tank, through a supply conduit and a thermal exchanger, through a thermal output zone, then back through the return conduit.

FIELD OF THE INVENTION

[0001] The invention relates generally to auxiliary thermal recovery for heating systems. Specifically, the invention relates to recovering thermal energy associated with effluent systems and applying it to heating systems.

BACKGROUND OF THE INVENTION

[0002] Increasing the efficiency of heating systems for dwellings and commercial buildings has been a longstanding challenge. It has been proposed to use a heat exchange fluid, such as water, to effect thermal transfer. Those of skill in the art will recognize that heat pumps, geothermal arrangements, and hydronic systems are among the many commercially available systems.

[0003] It is also known to enhance the efficiency of known systems by attempting to recover thermal energy that would otherwise be wasted. For example, U.S. Pat. No. 5,740,857 to Thompson et al. is directed to a heat recovery and storage device adapted to recover heat from warm waste liquid and transfer it to cooler supply water where the flows of both waste liquid and supply water are intermittent and not necessarily contemporaneous, and to store the warmed supply water until required for use. This invention comprises an internal high-thermal-conductivity waste liquid transmission pipe enclosed by a low-thermal-conductivity supply water reservoir pipe, the ends of the resulting storage reservoir being enclosed by end-plates incorporating an inlet and a discharge coupling means for installing the device into the waste liquid pipe of a building in place of a section of that pipe, the inlet and outlet coupling being so aligned that the internal surfaces of the waste liquid pipe from the building, the inlet coupling the heat recovery and storage device's internal waste liquid transmission pipe, the outlet coupling, and the waste liquid outlet pipe to the waste disposal means, respectively are aligned without obstruction so that the waste liquid flow is not impeded. The endplates may also be adapted to accommodate other pipes, such as that leading to the condenser of an air conditioner, from which heat may be transferred to the supply water. A cool supply water injection means is disposed in the lower portion of the reservoir and a tapping means for warmed supply water is disposed in the upper portion thereof. U.S. Pat. No. 5,736,059 to Mackelvie discusses an apparatus and system to recover heat from wastewater in a new or existing building comprising a convector heat exchanger with thermal storage that accepts wastewater of any temperature, an in-line separator to direct large solids away from the heat exchanger, a process to create turbulent flow in the tubing from which the heat exchanger is made, an automatically switched vibration base to improve heat transfer, an automatic flush system for the wastewater heat exchanger and a method of installation in slab-built buildings.

[0004] U.S. Pat. No. 5,791,401 to Nobile sets forth a heat recovery device adapted for use in the drain conduit of standard shower installations having a hot water line, a cold water line, means for mixing water from both lines to deliver water at a suitable temperature to a shower head, and a drain conduit for disposing of waste water passing through the shower installation, the heat recovery device transferring heat from the waste water to cold water flowing to the cold water line. The heat recovery device has a first conduit connected into the drain conduit of the shower installation, and a second conduit connected into the cold water line leading into the shower installation and either wrapped around or inserted within the first conduit so that the second conduit is in operative heat transfer relationship with warm waste water passing through the first conduit, so that the incoming cold water is preheated by heat recovered from the waste water and transferred to the cold water.

[0005] U.S. Pat. No. 5,730,208 to Barban is directed to an apparatus for exchanging heat between biothermal and geothermal ground heat sources and a heat pump for a building comprises a tank having a chamber for holding septic waste underground. The tank includes a heat conductive inner membrane for transferring heat to and from the waste. A fluid jacket located outside the chamber passes a heat transfer fluid adjacent a portion of the inner surface of the tank. Waste entry and exit piping transfers the waste to and from the chamber. Fluid inlet piping and outlet piping supplies the heat transfer fluid to and from the heat pump and the fluid jacket. When coupled to a heat pump in the heating mode, heat transfer fluid absorbs heat from biothermal sources within the tank and geothermal sources in and around the tank. In the cooling mode, heat transfer fluid conducts heat from a building to the tank and ground.

[0006] U.S. Pat. No. 4,184,856 to Thoren shows a domestic sewage system that discharges hot sewage from several sources in a building such as a home to a sewer. The home is here provided with a fan in the sewer vent to draw air from an air inlet in the sewer, through the sewer where the air becomes heated, and then through a heat exchanger where heat is removed from the air such as for room or water heating, and then out through the sewer vent.

[0007] Although these arrangements offer some advantages over standard heating and cooling systems, they are not optimally configured to recover as much thermal energy as possible, and fail to address problems such as friction and head. It can be seen from the foregoing that the need exists for a simple, inexpensive thermal energy recovery system that provides enhanced energy recovery and efficiency while overcoming the deficiencies of known arrangements.

SUMMARY OF THE INVENTION

[0008] These and other objects are achieved by providing a septic system thermal recovery mechanism including a septic tank. The tank has a top, a bottom, and at least one upstanding side wall joining the top to the bottom. The top, bottom, and at least one sidewall define an interior of the tank, and the at least one sidewall is devoid of angular corners. A septic inlet is adapted and constructed to conduct septic waste material into the interior of the tank, and a septic outlet is adapted and constructed to conduct septic waste material out of the interior of the tank. A thermal exchange fluid conduit is embedded in the at least one wall of the tank The thermal exchange fluid conduit is connected to a source of thermal exchange fluid. The mechanism is configured such that thermal exchange fluid can be circulated through the thermal exchange fluid conduit without traversing an angular corner and without contacting the interior of the tank.

[0009] The sidewall can be provided as a cast concrete wall, with the thermal exchange fluid conduit being PEX tubing embedded in sidewall in a spiral configuration at the time the sidewall is cast. The sidewall itself can be configured in any suitable form, such as a substantially contiguous cylindrical wall, or four walls in two substantially parallel pairs of sidewalls, the contiguous sidewalls being connected together with rounded connecting portions. The thermal recovery mechanism can also include a second thermal exchange fluid conduit embedded in the top of the tank.

[0010] In an embodiment, the mechanism can include first and second tanks constructed as described, with septic waste flowing from the first tank to the second tank. A thermal exchange fluid pump can be connected to circulate thermal exchange fluid sequentially through a return conduit, into a thermal exchange fluid conduit in the second tank, then through a first thermal exchange fluid conduit in the first tank, through a supply conduit and a thermal exchanger, through a thermal output zone, then back through the return conduit.

[0011] The features of the invention believed to be patentable are set forth with particularity in the appended claims. The invention itself, however, both as to organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in conjunction with the following drawings.

DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a schematic diagram of a thermal energy recovery system incorporating the principles of the present invention.

[0013]FIG. 2 is a schematic diagram of another embodiment of a thermal energy recovery system incorporating the principles of the present invention.

[0014]FIG. 3 is a schematic perspective view of a septic tank provided with a thermal energy recovery system incorporating the principles of the present invention.

[0015]FIG. 4 is a schematic sectional view of another embodiment of a septic tank provided with a thermal energy recovery system incorporating the principles of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0016]FIG. 1 illustrates a heating or cooling system 10 including a septic system 12 having a thermal energy recovery system incorporating the principles of the present invention. The system 10 uses a pump 14 to circulate a thermal exchange medium, for example, a thermal exchange fluid such as a glycol solution. The pump 14 sends fluid exchange medium from a supply conduit 16 past a thermal exchanger 18, where heat energy is either added to the fluid ( in the case of heating) or removed from the fluid (in the case of cooling), as is known in the art. The fluid then travels to a thermal output zone 20, which may be a radiator, in-floor system, or other suitable thermal output arrangement. The fluid then travels through a ground loop 21 as is known in the art, then through a return conduit 22 to the septic system 12 having a thermal energy recovery system, as will be described in detail below. The septic system 12 include a septic holding tank 24 that receives waste from a septic inlet 26 and outputs treated waste through a septic outlet 28. For heating purposes, such waste generally contains heat from its source, and fermentation of the waste within the tank 24 generates additional heat energy, providing a significant heat source during cold periods. The septic system can also act as a cooling element during warmer periods, since the tank is typically installed underground, where temperatures are usually significantly cooler than surface temperatures during warm periods.

[0017] An alternative system 30 including a septic system 32 having a thermal energy recovery system incorporating the principles of the present invention, is illustrated in FIG. 2. As with the FIG. 1 system, the system 30 uses a pump 34 to circulate a thermal exchange medium, for example, a thermal exchange fluid such as a glycol solution. The pump 34 sends fluid exchange medium from a supply conduit 36 past a thermal exchanger 38, where heat energy is either added to the fluid (in the case of heating) or removed from the fluid (in the case of cooling), as is known in the art. The fluid then travels to a thermal output zone 40, which may be a radiator, in-floor system, or other suitable thermal output arrangement. The fluid then travels through a ground loop 41 as is known in the art, then through a return conduit 42 to the septic system 32 having a thermal energy recovery system, as will be described in detail below. The septic system 32 include a first septic holding tank 44 that receives waste from a septic inlet 46 and outputs treated waste through a septic outlet 48. Waste from the septic outlet 48 travels through a second septic input 50 into a second tank 52. Waste from the second tank 52 passes through a second septic output 54. In use, the tank 44 will contain sludge, i.e., waste containing solids, and the tank 54 will contain liquid waste, i.e., gray water.

[0018] For heating purposes, such waste generally contains heat from its source, and fermentation of the waste within the tanks 44, 54 generates additional heat energy, providing a significant heat source during cold periods. The tank 44, being closer to the waste source, is generally warmer than the tank 54. Consequently, thermal exchange medium is directed first to the tank 54, then to the tank 44, and out through the supply conduit 36. As with the FIG. 1 embodiment, the septic system can also act as a cooling element during warmer periods, since the tank is typically installed underground, where temperatures are usually significantly cooler than surface temperatures during warm periods.

[0019] Construction of a tank 56 having a thermal energy recovery system incorporating the principles of the present invention is shown in FIG. 3. The tank 56 has a top 58, a bottom 60, and at least one upstanding side wall 62 joining the top 56 to the bottom 58, defining an interior 64 of the tank 56. A septic inlet 66 is adapted and constructed to conduct septic waste material into the interior 64 of the tank 56, and a septic outlet 68 is adapted and constructed to conduct septic waste material out of the interior 64 of the tank 56. A thermal exchange fluid conduit 70 is embedded in the sidewall 62 of the tank 56. The thermal exchange fluid conduit 70 is connected to a source of thermal exchange fluid via a return conduit 72. The mechanism is configured such that thermal exchange fluid can be circulated through the thermal exchange fluid conduit 70 and out of a supply conduit 74 without traversing an angular corner and without contacting the interior of the tank. To this end, in the FIG. 3 embodiment, the sidewall 62 is provided as a cast concrete wall, with a the thermal exchange fluid conduit 70 being polyextruded polyethylene (PEX) tubing embedded in sidewall 62 in a spiral configuration at the time the sidewall 62 is cast. The sidewall 62 can be configured in any suitable form, and here is shown as a substantially contiguous cylindrical wall, and can be fabricated from any suitable material, such as fiberglass, plastic, or composite materials. It is also contemplated that other shapes, such as oval or octagonal shapes, can be used.

[0020] The thermal recovery mechanism can also include a second thermal exchange fluid conduit 76 embedded in the top 58 of the tank 56. The conduit 76 performs in the same manner as the conduit 70.

[0021] An alternative tank 78 is shown in FIG. 4. The tank 78 includes four walls 80, 82, 84, and 86 in two substantially parallel pairs of sidewalls (80, 84 and 82, 86). The contiguous sidewalls are connected together with rounded connecting portions 88. Septic waste is brought in through an inlet 90 and output through an outlet 92. Thermal exchange fluid comes into a spirallyconfigured thermal exchange fluid conduit 94 via a return conduit 96 and exits via a supply conduit 98, as described in the FIG. 1 embodiment. A layer of insulation 100 can be provided to reduce heat transfer.

[0022] It is contemplated that various modifications can be made to the specific embodiments described. For example, the thermal exchange medium can be provided as any suitable substance, such as recirculating air in a forced-air system.

[0023] Although the present invention has been described with reference to specific embodiments, those of skill in the art will recognize that changes may be made thereto without departing from the scope and spirit of the invention as defined by the appended claims. 

What is claimed is:
 1. A septic system thermal recovery mechanism comprising the following: a septic tank having a top, a bottom, and at least one upstanding side wall joining the to the bottom, the top, bottom, and at least one sidewall defining an interior of the tank, the at least one sidewall being devoid of angular corners; a septic inlet adapted and constructed to conduct septic waste material into the interior of the tank; a septic outlet adapted and constructed to conduct septic waste material out of the interior of the tank; and a thermal exchange fluid conduit embedded in the at least one wall of the tank, the thermal exchange fluid conduit being connected to a source of thermal exchange fluid; whereby thermal exchange fluid can be circulated through the thermal exchange fluid conduit without traversing an angular corner and without contacting the interior of the tank.
 2. A septic system thermal recovery mechanism in accordance with claim 1, wherein the sidewall comprises a cast concrete wall, and the thermal exchange fluid conduit comprises PVC tubing embedded in the at least one sidewall in a spiral configuration at the time the sidewall is cast.
 3. A septic system thermal recovery mechanism in accordance with claim 2, wherein the at least one sidewall comprises a substantially contiguous cylindrical wall.
 4. A septic system thermal recovery mechanism in accordance with claim 2, wherein the at least one sidewall comprises four walls in two substantially parallel pairs of sidewalls, the contiguous sidewalls being connected together with rounded connecting portions.
 5. A septic system thermal recovery mechanism in accordance with claim 1, further comprising a second thermal exchange fluid conduit embedded in the top of the tank.
 6. A septic system thermal recovery mechanism comprising the following: a first septic tank having a top, a bottom, and at least one upstanding side wail joining the to the bottom, the top, bottom, and at least one sidewall defining an interior of the tank, the at least one sidewall being devoid of angular corners; a first septic inlet adapted and constructed to conduct septic waste material into the interior of the first tank; a first septic outlet adapted and constructed to conduct septic waste material out of the interior of the first tank; a second septic tank having a top, a bottom, and at least one upstanding side wall joining the to the bottom, the top, bottom, and at least one sidewall defining an interior of the tank, the at least one sidewall being devoid of angular corners; a second septic inlet adapted and constructed to conduct septic waste material from the first septic outlet of the first tank into the interior of the second tank; a second septic outlet adapted and constructed to conduct septic waste material out of the interior of the second tank; a first thermal exchange fluid conduit embedded in the at least one wall of the first tank; a second thermal exchange fluid conduit embedded in the at least one wall of the second tank; a thermal exchange fluid circulation assembly including a supply conduit, a thermal exchanger, a thermal output zone, and a return conduit; and a thermal exchange fluid pump connected to circulate thermal exchange fluid sequentially through the return conduit, through the second thermal exchange fluid conduit in the second tank, then through the first thermal exchange fluid conduit in the first tank, through the supply conduit and the thermal exchanger, and through the thermal output zone.
 7. A septic system thermal recovery mechanism in accordance with claim 6, wherein the first tank is adapted and constructed to contain sludge, and the second tank is adapted and constructed to contain gray water.
 8. A septic system thermal recovery mechanism in accordance with claim 1, wherein the respective sidewalls of the first and second tanks comprise cast concrete walls, and the thermal exchange fluid conduits comprise PVC tubing embedded in the at least one sidewalls in a spiral configuration at the time the sidewalls are cast.
 9. A septic system thermal recovery mechanism in accordance with claim 8, wherein the sidewalls of the first and second tanks comprise substantially contiguous cylindrical walls.
 10. A septic system thermal recovery mechanism in accordance with claim 8, wherein the sidewalls of the first and second tanks each comprise four walls in two substantially parallel pairs of sidewalls, the contiguous sidewalls being connected together with rounded connecting portions.
 11. A septic system thermal recovery mechanism in accordance with claim 6, further comprising a second thermal exchange fluid conduit embedded in the top of the tank.
 12. A method of constructing a septic system thermal recovery mechanism comprising the following: forming a septic tank having a top, a bottom, and at least one upstanding side wall joining the to the bottom, the top, bottom, and at least one sidewall defining an interior of the tank, the at least one sidewall being devoid of angular corners; securing a septic inlet to the tank at a position to conduct septic waste material into the interior of the tank; securing a septic outlet to the tank at a position to conduct septic waste material out of the interior of the tank; and embedding a thermal exchange fluid conduit in the at least one wall of the tank, the thermal exchange fluid conduit being adapted and constructed to be connected to a source of thermal exchange fluid; whereby thermal exchange fluid can be circulated through the thermal exchange fluid conduit without traversing an angular corner and without contacting the interior of the tank.
 13. A septic system thermal recovery mechanism in accordance with claim 12, wherein the step of forming the at least one sidewall comprises casting a concrete wall, and the step of embedding a thermal exchange fluid conduit comprises embedding PVC tubing in the at least one sidewall in a spiral configuration at the time the sidewall is cast.
 14. A septic system thermal recovery mechanism in accordance with claim 13, wherein the step of forming the at least one sidewall comprises forming a substantially contiguous cylindrical wall.
 15. A septic system thermal recovery mechanism in accordance with claim 13, wherein the step of forming the at least one sidewall comprises forming four walls in two substantially parallel pairs of sidewalls, the contiguous sidewalls being connected together with rounded connecting portions. 